Question

atomic number considerd to be more important than atomic mass

Answer 1

Because the atomic mass of two element can be same but each element have different atomic number

There is no fix increase in atomic mass but atomic number increase gradually by 1 each

Answer 2

Atomic No.(z) is considered to be more important than Atomic Mass(a) because according to the modern periodic table the atomic no. is the chemical and physical properties of an element are the periodic function of their atomic masses.

Atomic No. also provides the electronic configuration of the element.

Atomic No. helps us to know the No. of protons in a element.

In the modern periodic table we have arranged the the elements in increasing order of their atomic no. which prevents the need to place isotopes in a different group.